Guessing due date and HCG

Hi everyone ,

Recently had IUI on December 19, conception day, and at 14 dpo had blood work and confirmed.

HCG shows 850.3 today, nurse said the level was fine and is where it should be for a healthy pregnancy … but the nurse thinks I’m a day ish behind or so what they thought I should be.

I went and look at other apps and calculators, doctors office is saying I’m 5 weeks today , BUT other calculations are putting me at 4 w 5 days or 4 w 6 days … is there a chance they’ve miscalculated somehow ? Or is this all just a huge guessing game of BS ??

Has anyone else run into this issue with IUI or just conceiving naturally?

This is our rainbow baby we have been hoping for so I’m a little on edge just hoping for a healthy full term pregnancy.